A secondary battery has been widely used as a power source for mobile devices, such as a mobile phone, a laptop computer, and a camcorder. In particular, the use of a lithium secondary battery has been rapidly increased because the lithium secondary battery has high operating voltage and high energy density per unit weight.
Based on the construction of electrodes and an electrolyte, the lithium secondary battery may be classified as a lithium ion battery, a lithium ion polymer battery or a lithium polymer battery. In particular, the lithium ion polymer battery has been increasingly used because the lithium ion polymer battery has a low possibility of electrolyte leakage and can be easily manufactured.
The lithium ion polymer battery (LiPB) is configured to have a structure in which an electrode assembly manufactured by thermally welding electrodes (cathodes and anodes) and separators is impregnated with an electrolyte. Generally, the lithium ion polymer battery is configured to have a structure in which the electrode assembly is mounted in a pouch-shaped battery case formed of an aluminum laminate sheet in a sealed state. For this reason, the lithium ion polymer battery is often referred to as a pouch-shaped battery.
FIG. 1 is a view typically showing a general structure of a representative secondary battery including a stacked type electrode assembly.
Referring to FIG. 1, a secondary battery 10 is configured to have a structure in which an electrode assembly 30, including cathodes, anodes and separators disposed respectively between the cathodes and the anodes, is mounted in a pouch-shaped battery case 20, cathode and anode tabs 31 and 32 of the electrode assembly 30 are welded to two electrode leads 40 and 41, respectively, and the electrode assembly 30 is sealed in the battery case 20 in a state in which the electrode leads 40 and 41 are exposed to the outside of the battery case 20.
The battery case 20 is formed of a soft wrapping material, such as an aluminum laminate sheet. The battery case 20 includes a case body 21 having a hollow receiving part 23, in which the electrode assembly 30 is located, and a cover 22 connected to the case body 21 at one side thereof.
The electrode assembly 30 of the secondary battery 10 may be configured to have a jelly roll type structure or a stacked/folded type structure in addition to the stacked type structure shown in FIG. 1. The stacked type electrode assembly 30 is configured to have a structure in which the cathode tabs 31 and the anode tabs 32 are welded to the electrode leads 400 and 410, respectively.
The battery case 20 of the secondary battery is manufactured by pressing a sheet type base material, e.g. a base material of an aluminum laminate sheet, using a punch formed in the shape of a rectangular parallelepiped corresponding to the receiving part 23 and cutting the deformed sheet type base material so as to have a size corresponding to a cover in the longitudinal direction of the receiving part 23 and to a gas pocket in the lateral direction of the receiving part 23.
In recent years, however, a new type of battery cell is required in accordance with a slim type design trend or various other design trends. On the other hand, conventional battery cells are configured to include electrode assemblies having the same size or capacity and battery cases corresponding to the electrode assemblies. For this reason, in order to manufacture a battery cell of a novel structure in consideration of the design of a device, to which the battery cell is applied, it is necessary to reduce the capacity of the battery cell or change the design of the device so that the size of the device is increased.
In addition, electrical connection is complicated during change in design of the device, and therefore, it is difficult to manufacture a battery cell satisfying desired conditions.
Meanwhile, for a secondary battery, an electrode assembly is mounted in a receiving part, the receiving part is covered by a cover such that the receiving part is sealed, a contact portion between the cover and a main body is thermally welded, and an activation and aging step is performed. In order to remove gas generated at this time, the activation step is performed in a state in which a battery case having a gas pocket is primarily sealed. The gas is removed through the gas pocket, sealing is performed again according to the size corresponding to the receiving part, and the gas pocket is cut off. In this way, the secondary battery is manufactured.
In the pouch-shaped battery, however, a base material extends in a thickness direction of the receiving part in a state in which stress is inherent during pressing of the base material using a punch to form the receiving part with the result that it is difficult to accurately form a forming width of the receiving part. The thickness direction of the receiving part means the vertical direction or the direction in which the electrodes of the electrode assembly are stacked in the receiving part and the forming width of the receiving part means the width of the receiving part formed in the direction perpendicular to the thickness direction of the receiving part.
That is, when the base material is pressed to have the shape of a rectangular parallelepiped, wrinkles A or chlorosis B occurs at the corners of the receiving part as shown in FIGS. 2 and 3 with the result that moisture may penetrate into the battery.
Therefore, there is a high necessity for a technology that is capable of securing the space of a receiving part, in which electrode assemblies formed in various shapes are mounted, while fundamentally solving the above problems.